1. Field of the Invention
The present invention relates to a three dimensional (3D) braided composite tube, and more particularly, to a 3D braided composite tube with a narrower throat section and a manufacture method thereof.
2. Description of the Related Art
Braiding technologies are widely applied to the manufacture of fabrics, in which fiber yarns are interlaced woven in plane form. Braiding technologies also apply to the composite material and are widely used in many fields, such as vehicle, aviation, navigation, medical treatment, etc.
The composite material manufactured by lamination of fabrics is generally called two dimensional (2D) composite materials, in which the fabrics are used as reinforcement. The main drawback of the laminated 2D composite material is poor interlaminar properties. As an example, the insulation of a rocket nozzle is used in a high temperature (over 2000° C.) and shear force environment caused by hot air flow. Under such severe environment the laminated composite insulation would suffer pre-mature ply lift and/or spallation if the ply angle was not properly designed to avoid being parallel or vertical to air flow.
By adding thru-the-thickness reinforcement, the three dimensional (3D) woven composite material demonstrate much higher interlaminar strength over 2D woven composite material. However, most 3D technologies sacrifice the in-plane properties because of the reduction of the thru-the-thickness fiber content.
Therefore, the 3D braiding technology is introduced to improve interlaminar strength without sacrificing the in-plane properties of the composite structure. The fiber content of the 3D braided composite material is higher than that of the general 3D technologies, so the in-plane property is maintained. However, there are difficulties to manufacture hollow structures with a narrower throat section for used in, for example, a rocket nozzle by 3D braiding technologies.
FIG. 1 illustrates cross-section of a conventional rocket nozzle 100. For clearly showing the direction of the rocket nozzle 100, it also shows the rocket motor 110 in FIG. 1. The rocket nozzle 100 includes a convergent section 120, a throat section 130 and a divergent section 140, and the rocket nozzle 100 is basically a tube having larger radius at each end than the middle. The inner layer of the rocket nozzle 100 is an insulated layer 150 that reduces the heat via ablation to protect the shell 160.
FIG. 2 illustrates that the insulated layer 150 is manufactured on a mandrel 200 by a 3D braiding technology. Tension of fiber yarn 210 in the insulated layer 150 prevents it from contacting the mandrel 200 while braiding. The convergent section 220, the throat section 230 and the divergent section 240 of mandrel 200 are respectively correspond to the convergent section 120, the throat section 130 and the divergent section 140 of FIG. 1. The fiber yarn 210 in the insulated layer 150 being not able to contact to mandrel 200 make the radius of the throat section larger than desired, as a result, the propulsion of the rocket nozzle is reduced.
There thus exists a need and a demand for an improvement in the methods for making a 3D braided composite tube with a narrower throat section to overcome the difficulty in prior art.